The present invention relates to methods for assembling airfoils onto rotors and carriers therefor forming parts of a turbine and assemblies thereof and particularly relates to methods for securing buckets and nozzles in final fixed radial positions relative to the rotor and stationary carrier and assemblies thereof.
As well known in turbine technology, for example, steam turbines, a plurality of airfoils are arranged in an annular array about a wheel or rotor rim. Additionally, a plurality of airfoils, e.g., stator blades, are also arranged in an annular array about a fixed carrier forming part of a housing surrounding the rotor. The airfoils of the rotor and carrier form multiple axially spaced stages through which a dynamic fluid, e.g., steam, passes to drive the rotor. Typically, each airfoil has a generally dovetail-shaped base or shank which is received in a complementary-shaped groove in the associated component part. For example, the base of a bucket has a pair of axially extending flanges defining recesses along axially opposite sides of the base for disposition in a complementary-shaped groove on the rotor. Thus, the rotor groove has flanges receivable within the bucket recesses and recesses for receiving the flanges of the bucket base. Correspondingly, the airfoils forming the stator blades have bases with axially extending recesses and flanges which are complementary in shape to axially extending flanges and recesses of the carrier so that the bases of the stator airfoils can be disposed in the groove of the carrier.
To install the buckets along the rim of the rotor, a radial entry slot is formed in the rotor. The bases of the airfoils are passed through the entry slot and then advanced circumferentially along the groove, stacking the airfoil bases one against the other. For each fixed carrier (which is split into a top half and a bottom half), the airfoils are inserted at the horizontal split line of each half and slide in a circumferential direction along the groove in the carrier to stack the bases thereof one against the other. In order to slide the airfoils in a circumferential direction, however, radial clearance between the bases of the airfoils and the slots is required. It will be appreciated that because of the necessary radial clearance, the airfoils are also required to be fixed in a radial direction, as well as circumferential direction, in final position. Accordingly, there is a need for apparatus and methods for fixing the airfoils in a final radial position about the rotor or carrier.
In accordance with a preferred embodiment of the present invention, there is provided methods for facilitating final securement of the airfoils in fixed radial positions relative to the rotor and the carrier and assemblies thereof. The assembly includes a configuration of the grooves in the rotor and carrier, configurations of the bases of the airfoils generally complementary to the grooves and a plurality of pins. Two different tools for use during installation of the airfoils on the rotor and carrier are also provided as part of a method of assembly. Particularly, a circumferentially extending groove having a generally dovetail shape in a circumferential direction and comprising part of a rotor rim or a stationary carrier is provided. Additionally, a plurality of airfoils each having a base generally complementary in shape to the dovetail-shaped groove is provided. Thus, the bases of the airfoils are slidable in a circumferential direction along the grooves with a radial clearance whereby the bases of the airfoils may be stacked in an arcuate array thereof against one another upon installation in the groove. To finally position the airfoils relative to the groove and prevent radial movement, a retaining element is disposed between the bottom of the groove and the bottom of the base of each airfoil to displace and retain the airfoil in a generally radial direction into a final fixed radial position relative to the groove. Particularly, a recess is formed in the bottom of a rotor or carrier groove and a pin comprising the retaining element is driven by unique tools into the recess. The pin is generally cylindrical and has a flat along a side thereof. With the pin in the recess, the flat projects from the recess beyond the base of the groove and, when driven into engagement between the base of the airfoil and the bottom of the groove, the airfoil is located in its final fixed radial position.
One of the tools has a straight handle and a tool head terminating in an end generally corresponding to the shape of the pin. By driving a pin in a circumferential direction into the recess in the bottom of a groove between each airfoil base and the groove bottom, the pin fixes the airfoil into its radial final position. When the majority of the airfoils are stacked against one another in the groove, there is limited clearance for this first tool to drive the pin in a generally tangential direction into the groove to complete the installation of the remaining airfoils. Consequently, for the remaining airfoils, a second tool having an angled tool head and a tip corresponding to the shape of the pin end is provided. By inserting the second tool head into the groove with the back side of the tool head engaging along the recess in the groove bottom, a hammering action on the tool handle provides sufficient lateral force to drive the pin between the recess of the groove and the base of the airfoil forcing the airfoil into final position.
In a preferred embodiment according to the present invention there is provided in a turbine having an arcuate groove forming a generally dovetail shape in a circumferential direction forming part of a rotatable rotor rim or a stationary carrier and a plurality of airfoils each having a base generally complementary in shape to the dovetail-shaped groove and wherein the airfoil bases are slidable circumferentially along the groove with a radial clearance for stacking the airfoils in an arcuate array upon installation thereof in the groove, a method of finally radially positioning the airfoils relative to the groove, comprising the steps of (a) displacing an airfoil by sliding the airfoil base along the groove to a substantially final circumferential location within the groove and (b) inserting a retaining element between the bottom of the groove and a bottom of the base of the airfoil to displace the airfoil in a generally radial direction into a final radial position relative to the groove.
In a further preferred embodiment according to the present invention, there is provided a turbine comprising a turbine component having an arcuate generally dovetail-shaped groove extending in a circumferential direction, a plurality of airfoils each having a base generally complementary in shape to the shape of the dovetail-shaped groove, the dovetail-shaped groove and the dovetail-shaped airfoil bases having a radial clearance therebetween to enable displacement of the airfoil bases about the groove and an element disposed between the airfoil bases and a bottom of the groove to locate the airfoil in a fixed final radial position taking up the radial clearance between the airfoil bases and the groove.